VISION 199 



surfaces are all normal, in what way must the eye differ from the 

 normal eye? This condition is called near-sightedness, or myopia. 



(7) In case (5, 6), if a subject can read all of the letters expected 



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of the normal eye one credits him with F=-; but the eye may have 



accomplished the result at the expense of more or less effort. 



If the eye have a punctum remotum beyond infinity i. e., if the 

 rays of light from a distant object are not yet converged to a focus 

 by the time they reach the retina in the resting eye it will require 

 a certain effort of accommodation to produce a clear image. Such 

 is the condition in the far-sighted person; the condition is called 

 hyperopia. The term far-sightedness does not mean that the subject 

 can see farther than the average individual, but that he can see far 



objects more easily than he can see near objects. If a subject with 

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F=~ can see as clearly or more clearly when the +0.75 D. lens is 

 6 



in front of the eye, there is no reasonable doubt that hyperopia in 

 some form is present. 



(8) Let the subject direct the line of vision toward the center 

 of the chart for testing astigmatism. It is probable that not all of 

 the radiating lines will appear equally clear-cut and black, for most 

 persons have a small degree of astigmatism. If the lines are un- 

 equally clear, where are the clearest ones located? Do they describe 

 a diameter across the circle? If so, describe the location of the clear 

 diameter, degrees to 180 degrees being the horizontal diameter, and 

 90 degrees to 90 degrees the vertical one. 



(9) (a) If the subject has normal vision with no astigmatism 

 or normal vision despite a slight stigmatism, he may be given a better 

 conception of just what a moderate degree of stigmatism is by putting 

 a +1 D. cyl. lens before his eye; or a rather high degree of simple 

 astigmatism by trying +2 D. cyl. or +3 D. cyl. 



(6) How may the subject be made artificially hyperopic? 



(c) How artificially myopic? 



(II) To Test the Color Sense. Let the subject take the three 

 test colors light green, purple, and red and choose from the mass 

 of worsteds the colors which he considers similar ones, placing the 

 chosen color in the class to which it belongs. It is not difficult to 

 determine whether or not the subject has a defective color sense. 

 If, for example, he is red blind he will not see the red in the purple, 

 or related colors, but will classify these with the blues, while the 

 reds will be confused with the greens. 



